1. Field of the Invention
The present invention relates to a rotary compressor, and more particularly, to a muffler for attenuating a noise generated in operation of a rotary compressor.
2. Background of the Related Art
The compressor for compressing air or gas to a required pressure is used in an air conditioner or the like for compressing a refrigerant gas to a required pressure.
A related art rotary compressor will be explained with reference to FIGS. 1 and 2.
The related art rotary compressor is provided with a hermetic case 1 having a suction pipe 16 for drawing refrigerant and a discharge pipe 5 for discharging the compressed refrigerant, both connected thereto, a driving unit 6 in the case 1 for providing a rotating force, and a compression unit 10 for compressing gas. The driving unit 6 has a stator 2 and a rotor 3 of a motor mounted on an upper portion in the case 1. The rotor 3 is coupled to a shaft 4 for transmission of a rotating power to the compression unit 10. The rotor 3 has an eccentric portion 4a at a lower portion thereof. The compression unit 10 has a compression chamber `C` enclosed by a cylinder 11 forming a wall of the compression chamber `C`, and a main bearing 14 and a supplementary bearing 15 mounted at an upper side and a lower side of the compression chamber `C` respectively. The compression chamber `C` has the suction pipe 16 connected thereto for receiving refrigerant from outside of the compression chamber `C`. The cylinder 11 and the main bearing 14 have a discharge opening 11a and a discharge passage 14b formed therein respectively for discharging refrigerant, which discharge passage 14b is opened/closed by a valve(not shown). In the meantime, the eccentric portion 4a of the shaft is mounted in the compression chamber `C`, i.e., inside of the cylinder 11. There is a roller 12 fitted to an outside of the eccentric portion 4a for making a compression action as the eccentric portion 4a keeps making contact with an inside surface of the cylinder 11 following rotation of the eccentric portion 4a. And, there is a vane 13 mounted in the cylinder 11 to be always in contact with an outside of the roller 12 biased by a spring for dividing the compression chamber `C` into a high pressure portion and a low pressure portion. There is a muffler 20 above the main bearing 14 for attenuation of noise, which has a muffler discharge opening 21 for discharging a compressed gas received from a cylinder discharge opening 11a to an inside of the case 1.
The muffler will be explained with reference to FIGS. 3A and 3B.
The muffler 20 in a form of a cap has a boss hole 22 for passing a boss portion 14a of the main bearing 14, and recessed bolt fixing parts 23 in an outer circumference thereof for fastening the muffler 20 to the main bearing 14. The muffler 20 has a muffler discharge opening 21 for discharging the compressed gas flowed into the muffler 20, formed in outer periphery spaced from the boss hole 22.
The operation of the related art rotary compressor will be explained with reference to FIGS. 1 and 2.
Upon starting the rotary compressor, the rotor 3 of the motor is rotated, to rotate the eccentric portion 4a of the shaft, eccentrically rotating the roller 12 inside of the cylinder 11 in a state the roller 12 is in contact with the vane 13. The eccentric rotation of the roller 12 reduces a volume of the compression chamber `C`, compressing low pressure refrigerant flowed into the compression chamber `C` through the suction pipe 16 to a required pressure. The compressed high pressure refrigerant is discharged into the muffler 20 above the main bearing 14 through the cylinder discharge opening 11a and the discharge passage 14b of the main bearing, following operation of the valve. The high pressure refrigerant thus discharged into the muffler 20 is discharged into an inside of the case 1 through the muffler discharge opening 21. And the high pressure refrigerant discharged into inside of the case 1 is discharged outside of the rotary compressor through the discharge pipe 5 on top of the case 1 through gaps between the rotor 3 and the stator 2 or the case 1 and the stator 2.
FIG. 4 illustrates a pressure distribution in the muffler calculated according to a numerical analysis method, and FIG. 5 illustrates a kinetic turbulent energy distribution calculated according to the numerical analysis method, referring to which a flow state of the compressed refrigerant inside of the muffler 20 will be explained.
As can be known from FIGS. 4 and 5, though there is a small pressure distribution variation in overall in the muffler 20, a kinetic turbulent energy distribution exhibited has a great variation. Though the pressure affects a performance of the compressor, the kinetic turbulent energy affects to a noise of the compressor. This is because the kinetic turbulent energy is a velocity energy which is a square of a velocity, and, though a fluid noise is functions of pressure variation, speed variation, and density variation, the pressure variation and the density variation affects to the noise little, but the velocity variation is proportional to the noise generation, mostly.
That is, as shown in FIG. 5, it can be known that, though there is a slight variation of kinetic turbulent energy around the boss hole 22 in the related art muffler 20, there is a great variation of kinetic turbulent energy as it goes to an outer circumference of the muffler where the muffler discharge opening is positioned, that increases the noise.
The reason why there is a great variation of the kinetic turbulent energy in the vicinity of the muffler discharge opening 21 will be explained.
The gas compressed in the compression chamber `C` is discharged from the compression chamber `C` to the muffler 20 in a turbulent state at a fixed average speed. Therefore, the gas discharged into the muffler 20 has a centrifugal force exerted thereon from the average speed and a discharge speed, to form a main flow at an outer circumference of the muffler 20, with an increased gas speed. That is, as the compressed gas flows from an inner circumference to the outer circumference of the muffler 20, a gas flow speed is increased by the inertia until the gas is discharged through the muffler discharge opening 21 formed in the vicinity of the outer circumference of the muffler 20, that causes much noise.
Therefore, because the refrigerant flowed in the muffler has not an even kinetic turbulent energy distribution and is discharged outside of the muffler 20 through the muffler discharge opening 21 without consumption of much of the velocity energy, the refrigerant is involved in little amount of a pressure fluctuation and a speed reduced in the muffler 20. Thus, the related art muffler has a poor noise reduction performance, and shows a directional noise generation pattern according to a position of the muffler discharge opening.